UNIX and POSIX Standards

The ANSI C StandardANSIC Standard X3.159-1989

The difference between ANSI C AND K&R CFunction prototyping: * ANSI C : data-type function-name (data type parameter name,..) Ex: int f1(int a , int b);

* K&R C : data-type function-name (parameter name,..)

EX: int f1(a , b); int a, b;

Constant and volatile qualifiers * Present in ANSI C not in K&R C * const-implies data cant be changed /*here printf cant change the value of x */ int printf(const char* x,.) { }

Volatile qualifier : implies the compiler can make any optimization of the variable EX : char get_io() { volatile char* io_port=0x7777; char ch=*io_port; ch = *io_port; }

Wide character support and internationalization *support to store characters which occupy more than one byte *ANSI C defines SETLOCALE function *which helps to specify the format of date monetary and real number presentation

SETLOCALE

Category 1 Category 2 LC_TYPE en_US//USLC_MONETARY fr_FR//FrenchLC_NUMERIC de_DE//GermanLC_TIMELC_ALL

#include Char setlocale (int category, const char* locale);

Permit function pointers to be used without dereferencing

*ANSI C a function pointer can be used like a function

*K&R C requires the pointer to be de referenced to call the function

Feature test macros

_STDC_ : 1-if underlying system is ANSI C compliant 0-Otherwise_LINE_ : Physical line number of the module_FILE_ : filename of module where the symbol is present_DATE_ : date of compilation of the module_TIME_ : time of compilation of the module

#include int main() { #if __STDC__ == 0 && !defined(__cplusplus) printf("cc is not ANSI C compliant\n"); #else printf(" %s compiled at %s:%s. This statement is at line %d\n", __FILE__, __DATE__, __TIME__, __LINE__); #endifreturn 0; }

THE ANSI/ISO C++STANDARDWG21-ISO and ANSI X3J16 : ANSI C/ISO C++ standardVersion 3.0 report : c++ should have * classes * derived classes * virtual classes * operator overloading * template classes * template function * exception handling * io stream

ANSI C AND ANSI C++

ANSI C-default prototype if called before declaration or defn

-int f1() is same as int f1()

-no type safe linkage

ANSI C++- prototype is mandatory

-int f1() is same as int f1(void)

-type safe linkage

THE POSIX STANDARDSPosix.1 : IEEE 1003.1-1990 adapted by ISO as ISO/IEC 9945:1:1990 standard *gives standard for base operating system APIPosix.1b : IEEE 1003.4-1993 * gives standard APIs for real time operating system interface including interprocess communication

Posix.1c : specifies multi thread programming interface Other POSIX compliant systems*VMS of DEC*OS/2 of IBM*W-NT of Microsoft*Sun solaris 2.t*HP-UX 9.05

To ensure program confirms to POSIX.1 standard user should define _POSIX_SOURCE as #define _POSIX_SOURCE ORSpecify -D _POSIX_SOURCE to a C++ compiler

_POSIX_C_SOURCE : its value indicating POSIX version_POSIX_C_SOURCE value----Meaning 198808L---- First version of POSIX.1 compliance 199009L---- Second version of POSIX.1 compliance 199309L---- POSIX.1 and POSIX.1b compliance

#define _POSIX_SOURCE#define _POSIX_C_SOURCE 199309L#include #include int main() { #ifdef _POSIX_VERSION cout

POSIX ENVIRONMENTDifference between POSIX and UNIX * In UNIX C and C++ header files are included in /usr/include In POSIX they are just headers not header files and /usr/include neednot exist * UNIX Superuser has special previlege and the superuser ID is always 0 POSIX Doesnot support the concept of superuser nor the ID is 0

THE POSIX FEATURE TEST MACROS_POSIX_JOB_CONTROL The system supports BSD type job control_POSIX_SAVED_ID keeps saved set-UID and set-GID_POSIX_CHOWN_RESTRICTED If -1 user may change ownership of files owned by them else only users with special privilege can do so

_POSIX_NO_TRUNC If -1 then any long path name is automatically truncated to NAME_MAX else an error is generated_POSIX_VDISABLE If -1 then there is no dissabling character for special characters for all terminal devices otherwise the value is the disabling character value

#define _POSIX_SOURCE#define _POSIX_C_SOURCE 199309L#include #include

int main() {#ifdef _POSIX_JOB_CONTROL cout

#ifdef _POSIX_SAVED_IDS cout

#ifdef _POSIX_CHOWN_RESTRICTED cout

#ifdef _POSIX_NO_TRUNC

cout

#ifdef _POSIX_VDISABLE

cout

Certain constants defined in _POSIX_CHILD_MAX6 max number of child processes that can be created at any one time by a process_POSIX_OPEN_MAX16 max number of files that can be opened simultaneously by a process_POSIX_STREAM_MAX8 max number of I/Ostreams that can be opened simultaneously by a process

_POSIX_ARG_MAX4096 max size, in bytes of arguments that can be passed to an exec function call _POSIX_NGROUP_MAX 0 max number of supplemental groups to which a process may belong_POSIX_PATH_MAX 255 max number of characters allowed in a pathname

_POSIX_NAME_MAX14 max number of characters allowed in a filename_POSIX_LINK_MAX8 max number of links a file may have_POSIX_PIPE_BUF512 max size of block of data that can be automatically read from or written to a pipe file

_POSIX_MAX_INPUT255 max capacity, in bytes, of a terminals input queue_POSIX_MAX_CANON255 max capacity, in bytes, of a terminals canonical input queue_POSIX_SSIZE_MAX32767 max value that can be stored in a ssize_t- typed object_POSIX_TZNAME_MAX3 max number of characters in a time zone name

Long sysconf(const int limit_name);Long pathconf(const char* pathname,int flimit_name);Long fpathconf(const int fdesc,int flimitname);

Int res;If(res=sysconf(_SC_OPEN_MAX))==-1)perror(sysconf);Else cout

THE POSIX.1 FIPS STANDARDJob control : _POSIX_JOB_CONTROL must be definedSaved set-UID and set-GID : _POSIX_SAVED_IDS must be definedLong path name is supported _POSIX_NO_TRUNC != -1_only authorised user can change ownership _POSIX_CHOWN_RESTRICTED != -1

_POSIX_VDISABLE should be defined

NGROUP_MAX value should be at least 8

Read and write APIs should return the number of bytes transferred after the APIs have been interrupted by signals

The group id of newly created file must inherit group ID of its containing directory

THE X/OPEN STANDARDSX/Open portability guide, ISSUE 3 (XPG3) --- 1989X/Open portability guide, ISSUE 4 (XPG4) --- 1999The portability guide specifies a set of common facilities and C application program interface function to be provided on all UNIX-based open systems

QUESTIONS What are the major differences between ANSI C and K & R C? explain (10)What is POSIX standard? Give the structure of the program to filter out non-POSIX compliant codes for a user program (10)What is an API ? How are they different from C library functions ? Calling an API is more time consuming than calling a user function . Justify or contradict (5)

Write a POSIX compliant C/C++ program to check following limits (10)Maximum path lengthMaximum characters in a file nameMaximum number of open files per process What is POSIX standard? Explain different subsets of POSIX standard .write the structure of the program to filter out non-POSIX compliant codes for a user program (6)

Write a C++ program that prints the POSIX defined configuration options supported on any given system using feature test macros (8)

List out all POSIX.1 and POSIX 1b defined system configuration limits in manifested constants with complete time limit , minimum value and meaning (10)

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